Electric insulating bushing and glass therefor



July 4, 1950 A, MLEY I 2,513,958

ELECTRIC INSULATING BUSHING AND GLASS THEREFOR Filed Aug. 17, 1949 Fig.3.

Invefitor: Hevbert A.Omley,

by H i s Attorney.

Patented July 4, 1950 ELECTRIC INSULATING BUSHING AND GLASS THEREFORHerbert A. Omley, East Nassau, N. Y., asslgnor to General ElectricCompany, a corporation of New York Application August 17, 1949, SerialNo. 110,713

' 12 Claims. (01. 174-152) This invention relates to glass electricaldevices. More particularly, it relates to electric devices such asinsulating bushings and the like and to the glass used in such devices.

A major problem in connection with electrical glasses out of which glassbushings are cast has been to achieve a high degree of adhesion orsealing, between the glass insulator element and the metal alloy partsof the bushing assembly. Heretofore, considerable trouble has beenexperienced with lead-containing glasses in that ferrous alloys and leadglass tend to react chemically. This results in the deposition ofmetallic lead on the surface of the ferrous metal and produces pooradhesion between the metal and the glass. It has been proposed toprotectively precoat the metal parts to prevent lead deposition, butsuch operations are costly and time-consuming. It has also been proposedto use a glass composition such as that disclosed in the application ofU. W. Grigoriefl, Serial No. 772,983, filed September 9, 1947, nowPatent No. 2,478,626, and assigned to the same assignee as the presentinvention. The glasses disclosed therein have no lead and, hence, avoidthe defect outlined above which had previously been experienced.However, the beneficial effects of the above leadless glass areaccomplished only at the expense of using relatively large quantities ofexpensive lithium oxide-producing materials.

An object of this invention is to provide a bushing glass of desirableelectrical and physical characteristics which may be made from readilyavailable raw materials.

Another object of this invention is to provide a bushing oflead-containing insulating glass which will provide a permanentweather-resistant glass to metal seal with iron-nickel alloy.

Another object of the presentinvention is to provide a glass such thatit will form a fluidtight seal with an alloy containing 41 to 43 percentnickel and 57 to 59 percent iron.

Other objects will become apparent from a consideration of the followingdescription and the drawing, in which Fig. 1 is a longitudinal crosssection view of an electric bushing; Fig. 2 is a side elevation view ofanother type of electric bushing; and Fig. 3 is a graph showing thecoefiicient of elongation of the glass and metal parts of such bushings,

It has been found that the foregoing objects of the invention mayreadily be accomplished by employing in the manufacture of electricbushings having metal fittings of about 57-59 percent iron-41 to 43percent nickel alloy and characterized by permanent weather-resistingglass to metal seals a glass consisting substantially of about 56 to 62percent silica, 19.5 to 24 percent boric oxide, 2 to 3 percent lithiumoxide, 4.5 to 7 percent sodium oxide, 1 to 4 percent potassium oxide, 3to 8 percent alumina, 0.1 to 1 percent calcium oxide and 3 to 7 percentlead oxide.

The raw materials, or batch ingredients, which determine the finalcomposition of the glass, are fused and reacted in a suitableglass-making furnace at a temperature in the range of from about 1100 C.to about 1350 C. and preferably at about 1300 C. Heat may be supplied tothe mix by any suitable means, but that afforded by an electric furnaceis preferred. The time fusion and reaction will vary, depending upon thetemperature. At the preferred temperature of 1300 C., twelve hours issufficient.

The analyses of the glasses produced by the practice of this inventionare substantially as follows, all proportions being in percent byWeight:

. Per cent Silica (SlOz) 56.0 to 62.0 Boric oxide (B203) 19.5 to 24.0Lithium oxide (L120) 2.0 to 3.0 Sodium oxide (NazO) 4.5 to 7.0 Potassiumoxide (K20) 1.0 to 4.0 Alumina (A1203) 3.0 to 8.0 Calcium oxide (CaO)0.1 to 1.0

Lead oxide (PbO) I 3.0 to 7.0

The preferred glass has a percent by weight composition substantially asfollows:

Calcium oxide (CaO) 0:1 Lead oxide (PbO) 5.0

The fused glass may be poured directly into molds at a temperature ofabout 1250 C. to 1300 C., and preferably at about 1280 C. Metal insertsor bodies are placed in the mold and the molten glass poured around themto form an integral product. The metal inserts to be used with the aboveglass should have a coefiicient of linear expansion corresponding tothat for an iron-nickel alloy containing 57 percent to 59 percent ironand 41 percent to 43 percent nickel. This alloy has a coefficient oflinear expansion of about 5.5 x 10 to 5.6 x 106 at from about 25 C. to300 C. This value matches that of the above glass and insures apermanent fluid tight seal between the glass and metal. Preferably,though not necessarily, the glass part after casting should be annealed.

The glass of the present invention is composed of a balance ofconstituents, each of which, in addition to producing a desiredcoefiicient of linear expansion, contributes to the workability or othercharacteristics of the glass. For example, the lithium oxide enhancesthe wetting ability of the glass and thus contributes to a P rfect seal.It also makes the glass more fluid. The lead oxide also promotesfluidity, and, in conjunction with the lithium oxide, enables the glassto be poured through a restricted opening or orifice as small asthree-eighths of an inch in diameter at pouring temperatures rangingfrom about 1250 C. to 1300 C. The calcium oxide counteracts any tendencytoward the formation of stones, cords and other like defects in theglass. Weather-resistance of the composition is increased by thepresence of alumina in a more substantial amount. The boric oxidecontributes to the desirable electrical resistivity and other electricalcharacteristics, as does the silica.

Typical of the insulating bushings which may be fabricated or molded ofthe present glass are those shown in Figs. 1 and 2. The bushingillustrated in Fig. 1 includes hollow stud l, which is threaded as shownat the upper extremity. Stud is brazed or otherwise suitably joined withcollar 2 which latter, in turn, is embedded in the glass insulator 3.Also embedded in the glass insulator 3 is the rim of lower collar 4.Collar 4 also serves as a means whereby the entire bushing assemblymaybe mounted, as by Welding, brazing, soldering, etc. to base 5, whichmay be the container for an electrical device or any other mounting onwhich it is desired to place the bushing. Metal tube 6, which passeslongitudinally through the insulator 3 and is held in position at theupper end by thimble I, may serve as a conduit for a conductor which isnot shown. This conductor may be fixed to the stud l in any conventionalway. In addition to positioning tube or sleeve 6, thimble 1 serves toshield portions of collar 2 from contact with fused glass during thecasting process, thus permitting expansion and contraction of thebushing parts without damage. Shield 8, at the lower end of theinsulator, serves a similar purpose with respect to collar 4.

Fig. 2 shows a modified bushing which consists of three terminal studs9, l0, and H, which are, respectively, provided with collars 12, I3 andM. The rims of these collars, as in the case of collars 2 and 4 withrespect to insulator 3, are embedded in the cast glass insulator I5.These collars are also provided with shields similar in style andpurpose to part I. Basal collar l5 also has a flange (not shown) whichis embedded in glass insulator l5 during casting. Flange ll of collar I6is joined by any suitable means known in the art to part [8, which maybe the container of a capacitor, transformer, other electrical device,or any desired base.

The glass of the present invention is admirably suited for the purposedescribed. The coeificient of linear expansion or rate of linear changeof the glass, as indicated at 18 in Fig. 3, matches almost perfectly, asindicated at 20, that of the 58 percent iron-42 percent nickel alloyinserts over a. wide temperature range. The very slight differences inexpansion and contraction characteristics are not sufiicient to causecracking of the glass or other difficulty either during manufacture oruse. As a matter of fact, the heat shock of the present bushings is verygood. For example, bushings constructed as described and about sixinches long were repeatedly heated to 75 C. and suddenly deluged withcold water at a temperature of 15 C. without showing any signs offailure.

The weatherability of the present glass and the glass to metal sealswhich it forms also contributes to its desirability in the present use.

The electrical characteristics of the glass used in the present bushinglend themselves readily to use in bushings, as Will be evident from thetabulation below:

Resistivity 6.0x 10 ohms/-3 cm. Dielectric constant 7.15 Power factor0.15

The bushings of this invention may be used alone or in connection withany of the known gaseous, liquid or solid dielectric media. The metalinsert-glass seal has been found to resist gas leakage indefinitely attemperatures ranging from 40 C. to 115 C. The above seals have beenfound useful in resisting the effects of the halogenated hydrocarbondielectrics which have more of a deteriorating and leaking tendency thando mineral oils, for example.

In order to provide the maximum protection against deterioration ofhalogenated hydrocarbon dielectrics used in conjunction with bushingsemploying the present glass it is preferable, though .not necessary, toinclude in the above glass compositions from 0.5% to 1.0% and preferablyabout 0.9 percent, by weight, of manganese dioxide (MnO2.) and 0.1% to0.3% and preferably 0.2% iron oxide (Fe20a) the P content being loweredaccordingly. The additives impart an amber-like color to the otherwisegreenish glass and prevents any tendency toward decomposition of theabove-type dielectrics by sunlight by screening out rays of harmfulwavelength without altering the other favorable characteristics of theglass.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A glass suitable for casting purposes comprising by weight 56 to 62percent S102, 19.5 to 24 percent B203, 2 to 3 percent Li20, 4.5 to '7percent Na20, 1 to 4 percent K20, 3 to 8 percent A1203, 0.1 to 1 percentCaO and 3 to '7 percent PhD.

2. A glass suitable for casting purposes consisting substantially byweight of 56 to 62 percent Si02, 19.5 to 24 percent B203, 2 to 3 percentLi20, 4.5 to 7 percent Na20, 1 to 4 percent K20, 3 to 8 percent A1203,0.1 to 1 percent CaO, 3 to 7 percent PbO and 0.5 to 1.0 percent MnO2.

3. A glass suitable for casting purposes comprising by weight 58 percentSiO2, 21 percent B203, 2 percent Li20, 5.5 percent Na20, 2.4 percentK20, 6 percent Al203, 0.1 percent CaO and 5 percent PbO.

4. A glass suitable for casting purposes consisting by weightsubstantially of 58 percent SiOz, 21 percent B203, 2 percent Li20, 5.5percent NazO, 2.4 percent K20, 6 percent A1203, 0.1 percent CaO,4.1'percent Pb0 and 0.9.percent MnO2.

5. A glass having a thermal coeflicient of expansion of from 5.6 x 10comprising by weight 58 percent S102, 21 percent B203. 2 percent L120,

5.5 percent Na20, 2.4 percent K20, 6 percent A1203, 0.1 percent Ca andpercent PbO.

6. A glass composition having sufficient fluidity when heated to about1250 C. to 1300 C. to flow when cast through an orifice of aboutthreeeighths inch diameter and to hermetically seal to metal membersconsisting of about 57 to 59 percent iron and about 43 to 41 percentnickel, said glass comprising 56 to 62 percent Si02, 19.5 to 24 percentB203, 2 to 3 percent Li20, 4.5 to '7 percent Na20, 1 to 4 percent K20, 3to 8 percent A1203, 0.1 to 1 percent Ca0 and 3 to 7 percent PhD.

7. A glass having approximately the same rate of linear expansion over atemperature range of about 25 C. to 500 C. as an alloy consisting ofabout 41 to 43 percent nickel and 57 to 59 percent iron and capable offorming a fluid-tight seal with said alloy, comprising by weight 56 to62 percent S102, 19.5 to 24'percent B203, 2 t0 3 percent Li20, 4.5 to 7percent Na20, 1 to 4 pering an insulating member of glass comprising 58percent S102, 21 percent B203, 2 percent L120, 5.5 percent Na20, 2.4percent K20, 6 percent A1202, 0.1 percent 020 and 5 percent PbO andcooperating electrical terminal members consisting of an alloy of 41 to43 percent nickel and 57 to 59 percent iron embedded in part in saidcent K20, 3 to 8 percent A1203, 0.1 to 1 percent CaO and 3 to '7 percentPbO.

8. A bushing for an electric device comprising an insulating member ofglass comprising 56 to 62 percent Si02, 19.5 to 24 percent B203, 2 to 3percent Li20, 4.5 to '7 percent Na20, 1 to 4 percent K20, 3 to 8 percentA1203, 0.1 to 1 percent Ca0 and 3 to 7 percent Pb0 and cooperatingelectric terminal members consisting of an alloy of 41 to 43 percentnickel and 57 to 59 percent iron embedded in part in said glass.

9. A bushing for an electric device comprislass.

10. A bushing for electrical purposes having an insulating member ofglass comprising the following constituents: 58 percent $102, 21 percentB203, 2 percent Li20, 5.5 percent Na20, 2.4 percent K20, 6 percentA1203, 0.1 percent Ca0 and 5 percent PbO.

11. A bushing for an electric device comprising an insulating member ofglass consisting substantially of 56 to 62 percent Si02, 19.5 to 24percent B203, 2 to 3 percent L120, 4.5 to 7 percent M220, 1 to 4 percentK20, 3 to 8 percent A1203, 0.1 to 1 percent 0210, 3 to 7 percent Pb0 and0.5 to 1 percent Mn02 and cooperating electric terminal membersconsisting of an alloy of 41 to 43 percent nickel and 57 to 59 percentiron embedded in part in said glass.

12. A bushing for electrical purposes having an insulating member ofglass containing substantially the following constituents: 58 percentSi02, 21 percent B203, 2 percent Li20, 5.5 percent Na20, 2.4 percentK20, 6 percent A1202, 0.1 percent Ca0 and 4.1 percent PhD and 0.9percent Mn02.

HERBERT A. OMLEY.

No references cited.

